Maryland Geological Survey 381 



the dorsal lobe, and to be somewhat smaller than the corresponding sinuses, 

 except the second and third. The dorsal or siphonal lobe is very wide and 

 deeply forked. The third lateral lobe, or fourth counting the dorsal, is 

 larger than any other, with two large lateral processes and a bifid 

 extremity. The others are generally trifid to the fifth or sixth, beyond 

 this a few of them are bilateral with two divisions on each side ; some of 

 the inner ones are long and clavate, with three or four slight projections, 

 while the two inner ones are only serrate on the sides with a perceptibly 

 swollen extremity. There are intermediate lobes between all the prin- 

 cipal ones, except the last two, on the largest specimen in hand, but they 

 vary in size and complication according to their position; that dividing 

 the first sinus being about equal in form and size to the seventh lateral 

 lobe. The first sinus is large and broad, each of its main divisions about 

 equal in size to the third sinus." — "Whitfield, 1892. 



Placenticeras placenta is known within the area under discussion only 

 from the Chesapeake and Delaware Canal, the general area of the type 

 locality. The individuals are all of them from a ferruginous matrix, and 

 though far from perfect the characteristic sutures are sufficiently distinct 

 on all the fragments so that there is no doubt about their determination. 



Occurrence. — Matawan Foeiiatiox. Posts 249, 208, 105, Chesa- 

 peake and Delaware Canal, Delaware; ? Arnold Point, Anne Arundel 

 County, Maryland. 



Collections. — Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences. 



Outside Distribution. — Magothy Formation.. Cliffwood clay, New 

 Jersey. Matawan Formation. Merr-hantville clay marl, Woodbury clay, 

 Marshalltown clay marl, Wenonah sand, New Jersey. Pierre. Western 

 Interior, ? Ripley Formation. Tennessee (Morton). Austin Chalk. 

 Texas, Aff. Ammonites guadaloupa? Eoemer. Trichinopoli Formation. 

 Southern India, Aff. Ammonites guadaloupw Eoemer. 



